Continuous casting of non-ferrous metals



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United States Patent Othce 3,425,482 Patented eb. 4, 1969 3,425,482CONTINUOUS CASTING F NON-FERROUS METALS Alfons Capaul, Sierre,Switzerland, assignor to Swiss Aluminium Ltd., Chippis, Switzerland, aSwiss corporation Filed June 21, 1966, Ser. No. 559,290 Claims priority,application Switzerland, June 23, 1965, 8,819/65; Sept. 8, 1965,12,543/65 U.S. 'Cl. 1644 Int. Cl. B22d 11/10, 17/32; B22c 19/04 7 ClaimsABSTRACT OF THE DISCLOSURE This invention relates to the continuouscasting of nonferrous metals, and is particularly applicable to thecasting of aluminum and aluminum alloys, utilizing a float or floats toregulate the flow of metal to the mold.

In the continuous casting of slabs of aluminum or aluminum alloys to berolled in a rolling mill and of round bars every effort is made toobtain as smooth as possible a surface and the thinnest possible layerof columnar crystals at the surface of the strand and for this purposethe strand must be cooled very rapidly. Especially in the case of slabsto be rolled in rolling mills, it is desirable to reduce as far aspossible the thickness of the surface layer, which subsequently has tobe removed by a machining operation, for example by milling so that theloss of metal is kept to a minimum. In casting metal of anodic oxydationquality, that is to say a metal which can subsequently be anodicallyoxydized, in the form of sheet or profiled sections, a surface isrequired which does not produce streaks, spots or the like during theelectrolytic oxydizing process, and for this reason also it is highlydesirable to arrange that the surface layer containing columnar crystalscan be removed reliably by machining the surface to the least possibledepth.

When using a method of continuous casting in which there is a float onthe liquid metal in the mold to act as a valve controlling the flow ofliquid metal from a nozzle or nozzles to the mold, a surface layer ofthe required nature can be produced for example by using a high speed ofdescent of the strand, or by casting the strand with a low meniscus inthe mold, that is to say with a low height of metal in the mold.

Continuous casting with a high strand speed can, however, easily resultin a rupture of the solidified wall of the strand, particularly in thecase of a slab suitable for subsequent rolling. This technique cantherefore be applied only in certain circumstances that is to say onlyin the casting of strands of comparatively small cross-section, or incasting rods or plates.

The other technique in which the strand is cast with a low meniscusheight, does not involve any risk of rupture, even when the product fromthe mold is an aluminum slab for the subsequent rolling, with across-section of 800 x 150 mm. or more.

Experiments have shown, however, that in the continuous casting of slabshaving a cross-section of 800 x 150 mm. or more, and of round barshaving a diameter of 200 mm. or more, using the customary procedures, itis very diflicult to use a meniscus height of less than 50 to 60 mm.above the bottom of the mold, because there is not a sufficiently greatdistance between the float and the dummy bar that closes the mold bottomwhen the casting operation begins. If this distance is too small thefloat tends to become frozen in the solidifying metal.

It is accordingly among the principal objects of the invention to avoidthe drawbacks of the prior art.

It is another object of the invention to provide for special castingoperation steps and conditions to obtain the desired characteristics inthe casting that emerges from the mold.

It is a further object of the invention to provide for a continuouscasting process using a float for the purpose described earlier wherein,when the casting operation begins with a dummy bar closing the bottom ofthe mold, the nozzle or nozzles and the float are located so far abovethe bottom of the mold as to ensure that the molten metal rises to alevel at which the float does not freeze into the solidifying metal,and, just after the dummy bar has started to move downwards, thedistance between the nozzle or nozzles and the bottom of the mold isreduced for more than 10 mm., by which then is obtained the desiredmeniscus height relative to the bottom edge of the mold.

It is still another object of the invention to control the relativedistance of the float, and of the nozzle or nozzles and tundish, withrelation to the bottom of the mold. The distance involved here is thus arelative one and can be changed either by changing the level of thenozzle or nozzles or by changing the level of the mold, or by changingboth these levels. For example when casting an aluminum slab of largecross-section for subsequent rolling, initially the meniscus height canbe from 60 to mm. above the bottom of the mold and subsequently bereduced to a height of between 25 and 40 mm.

Hitherto in the vertical continuous casting of aluminum slabs of largecross-section the smallest practicable distance has been 50 to 60 mm.,so that the distance of the outlet end of the feed nozzle or nozzlesabove the bottom of the mold has been just a little more than that. Atthe start of casting operation, the mold was quickly filled with metalup to a height of 50 to 60 mm. above its bottom and at this height thefloat closed the nozzle or nozzles. As soon as the molten metal hadsolidified sufiiciently the descent of the dummy bar was commenced,taking the strand with it at a predetermined speed. The height of thenozzles and therefore of the meniscus did not change subsequently. Usinga meniscus height of from 50 to 60 mm. above the bottom of the mold, itis not possible to obtain the desired rapid solidification of the metal,and hence the resulting surface of the strand has transverse ridges,cold-set places and the like, and moreover the surface layer containingcolumnar crystals is rather thick. Under these circumstances it ispractically impossible to produce an aluminum slab which cansubsequently be rolled satisfactorily without first removing some of themetal on the Wide faces of the slab by a machining operation.

It is still another object of the invention to provide a continuouscasting process that permits aluminum or aluminum alloy slabs and roundbar stock to be made for example of aluminum/manganese and low alloyaluminum/magnesium, to be cast with a smooth surface, because a very lowmeniscus is used in the mold during the main part of the castingoperation. The slabs thus produced can be rolled into sheet of anodizingquality, because the surface layer of columnar crystals is thin anduniform and can be removed reliably by milling to a comparatively smalldepth.

A further advantage of the process in accordance with the invention isthat the pouring temperature range can be greater than that permissiblehitherto, without giving rise to cold-set places or a thicker surfacelayer of columnar crystals. In the case of pure aluminum for example thepouring temperature range can be increased upwards by about 10 C. anddownwards by about 10 C. to 15 C., which corresponds to a doubling ofthe range. Moreover, when pouring aluminum/manganese and low alloyaluminum/magnesium, a smoother surface is obtained because there is muchless sweating out.

In the casting of aluminum slabs for subsequent rolling, having across-section of at least 800 x 150 mm., in accordance with a stillfurther object of the invention the mold and the strand are cooled insuch a way that the sump of molten metal in the mold is substantiallyrectangular as seen from above and the thickness of the solidified crustwithin the mold is substantially the same along both the long and shortsides of the slab.

Examples of the process in accordance with the invention will now bedescribed with reference to the accompanying drawings in which:

FIGURE 1 is a diagrammatic plan view of the top of the strand in themold during a continuous casting process, indicating in a solid curvedclosed solid line the configuration of the metal sump in accordance withthe prior art, and in broken lines in accordance with the instantinvention;

FIGURE 2 is a fragmentary vertical sectional view through part of oneexample of a continuous casting machine for carrying out the process inaccordance with the invention;

FIGURE 3 is a plan view of the machine shown in FIGURE 2;

FIGURE 4 is an elevational view of a float forming part of the machineshown in FIGURES 2 and 3;

FIGURE 5 is a plan view of the float shown in FIG- URE 4;

FIGURES 6 to 8 are details of the machine shown in FIGURES 2 and 3;

FIGURE 9 is a plan view of the mold forming par of the machine shown inFIGURES 2 and 3;

FIGURE 10 is a sectional view taken along the line B-B of FIGURE 9;

FIGURE 11 is a sectional view taken along the line 0-6 of FIGURE 9;

FIGURE 12 is a side elevational view of a device for raising andlowering the height of the meniscus of the molten metal in the mold, thedevice forming a modification of the machine shown in FIGURES 2 and 3;

FIGURE 13 is a plan view of the modified device shown in FIGURE 12;

FIGURE 14 is a schematic diagram of a hydraulic mechanism and conduitoperating the device shown in FIGURES 12 and 13;

FIGURE 15 is a vertical sectional view of a part of a modified machineshowing a device for raising and lowering the mold;

FIGURE 16 is a plan view of the device shown in FIG- URE 15; and,

FIGURE 17 is a diagram of a hydraulic conduit of the device shown inFIGURES 15 and 16.

Referring to FIGURE 1, a mold is shown at 10 and a continuous line 11represents the edge of the sump of liquid metal in the mold at a leveljust under the surface of the melt. FIGURE 1 shows how, in theconventional continuous casting process, the molten metal solidifiesmuch more rapidly near the four corners of the strand than it does nearthe center portions of the long and short sides. This effect has beencalled running cold at the corners. There is a good deal of cold setnear the corners. In contrast to this, a broken line 12 represents theedge of the sump of liquid metal in the strand during a process inaccordance with the invention, in which the cooling of the mold andstrand is regulated to obtain this effect. Here the liquid sump issubstantially rectangular as seen from above and the four edges of thestrand run true. There is no premature cold setting of the short sidesand the height of the meniscus can be lowered to about 35 mm. above thebottom of the mold without the molten metal breaking through, forexample, at a place near the middle of a face of the strand.

The cooling arrangements for the short sides of the strand arepreferably separate from those for the long sides. Moreover, in thisexample, the dilferential cooling is further encouraged by usingdifferent spacing and different diameters for spray holes from whichwater is sprayed onto the short and long sides of the mold and strand.

In the continuous casting machine shown in FIGURES 2 to 14, the distanceof the meniscus above the bottom of the mold is adjusted by raising andlowering a tundish with nozzles through which the metal is supplied tothe mold.

As shown in FIGURES 2 and 3 a tundish 13, is supported on the shortsides 16 of a rectangular slab mold 17, by means of a cranked beam 14and lifting devices 15. In FIGURES 2 and 10 the short sides 16 of themold are shown in section. The long sides of the mold are shown at 18. Adummy bar 20 is mounted on a raising and lowering piston 21.

Example In this example the internal dimensions of the mold are 1020 by265 mm., to produce slabs having a crosssection of 1000 x 260 mm. Theinternal wall 19 of the mold is in this example smooth, but it mayalternatively be vertically fluted. This wall has a height of mm.

The apparatus for supplying the molten metal to the mold comprises thetundish 13 having a body 22, of grey cast iron which is coated insidewith mold wash or facing composition. The molten metal reaches thetundish 13 from a pouring spout 23, and leaves the tundish through twooutlet nozzles 24, from where it flows on to raised bafile plates 26 inthe bottom of a float 25. The baflle plates 26 act in conjunction withthe nozzles 24 to regulate the flow of molten metal, the flow beingstopped when the meniscus in the mold reaches a predetermined maximumheight in relation to the nozzles 24. At the beginning of the castingoperation the pouring spout 23 is disposed horizontally, so that whenthe tundish 13 is subsequently lowered the spout does not take up toosteep an angle.

The float 25 is supported by its ends 27 on angle brackets 28, which arethemselves supported from the cranked beam 14, by means of slotted bars29 and bolts 30 with nuts. The float 25 can be raised and lowered,relative to the cranked beam 14 by means of slots 31 in the bars 29 andthe angle brackets 28.

The construction and operation of each of the lifting devices 15 arebest described with reference to FIGURES 6, 7 and 8. Actuation of alever 32 rotates cam discs 33 with the result that a support 37 for thecranked beam 14 is raised or lowered, by means of rollers 34, a rollersupport 35 and a slide plate 36. In this movement, the plate 36 and thesupport 37 are guided by sleeves 38 which are fixed to the plate 36, andfit over and slide on pins 39.

The raising and lowering of the tundish 13 must of course take placeequally at both sides of the machine. This equalization of movement isensured by a mechanical stop system 40 which functions in conjunctionwith a series of holes 41, arranged to form a scale. Before actuatingthe lever 32, the operator first pushes a lever 42 to draw a pin 43 outof one of the holes 41. As soon as the lever 32 has been rotated as faras is required, the lever 42 is released and the point of the pin 43moves under the action of a spring 44 and engages in another of theholes 41, so that the lever 32 is locked. The levers 32 on both sides ofthe machine are actuated successively and are moved through equalangles.

In the mold 17 shown in FIGURES 2, 3, and 9 to 11 the long sides 18consist of hollow extruded sections made of aluminum/magnesium/siliconalloy. Cooling water is admitted to the interiors 46 of the hollowsections through connections 45, and issues through bores 47, whichspray the cooling water against the long sides of the strand as itemerges from the mold. The water is admitted to both ends of the hollowsections and therefore a region of higher pressure is produced near thecenter portion of the sections. This results in a greater cooling effecthere. The distribution of the cooling is further influenced by theabsence of bores for 2 /2% of the length of the sections 18 at bothends. The first bores situated at each end along the first 8% of thelength hollow sections, starting from the end and moving towards themiddle, each have a diameter of 2 mm., whereas the bores nearer themiddle have diameter of 2.5 mm. each. The short sides 16 of the moldconsist of angle sections in the form of aluminum/ magnesium/ siliconalloy castings. These members are cooled by a spray of water issuingfrom a spray tube 48, which has two rows of spray holes so arranged thatthe cooling water is directed, both on to the angle section member andalso on to the face of the strand itself just below the bottom edge ofthe mold. The cooling water is supplied to the stray tube 48 through aconnection 49, and the supply of water is controlled by a valve 50. Thefour sides of the mold are screwed together and are located relativelyto each other by dowel pins. The inner surfaces 19 are machined smooth.The mold is mounted on its supports by means of brackets 51.

FIGURES 4 and 5 show how the float 25 is constructed so that the moltenmetal issues horizontally towards the narrow sides of the mold. Thefloat is made of black iron plate 1.5 mm. thick coated with mold washcomposition.

Before the beginning of the casting operation, the tundish body 22 andthe pouring spout 23 are removed and the float 25 is adjusted in heightrelative to the cranked beam by moving the supporting brackets 28 up ordown, that is to say the float is set to set the gap between the nozzles24 and the baffle plate 26 when the tundish body 22 is replaced. Thewhole tundish and float assembly is then raised to its highest positionby actuating the lifting devices by means of the levers 32. As alreadymentioned, at the beginning of the casting operation the level of themeniscus of the melt must be high in the mold, in order to prevent thefloat from becoming frozen in near the bottom of the mold. As soon asthe surface of the melt has risen far enough to lift the float off thebrackets 28, that is to say as soon as the float is floating, thelowering of the dummy bar on the supporting piston 21 may be commenced.After the strand has emerged from the mold for a length of about 5 cm.the tundish 13 with the nozzles 24 and the float 25, is lowered slowlyuntil the height of the meniscus level above the lower edge of the moldhas decreased to the distance required for the remainder of the castingoperation. This lowering must be effected evenly, and this can be donewithout difficulty with the help of the rows of holes 41. As soon as therequired meniscus height is obtained, the levers 32 are locked.

Towards the end of the casting operation the tundish and float assemblymust be raised'again, to prevent it from freezing in, This is done inone movement by means of the levers 32, which lifts the float out of thepool of molten metal in the mold. This lifting movement also causes theresidue of molten metal in the pouring spout 23 to run back into thefurnace or ladle.

When the series production of ingots is required the machine shown inFIGURES 2 and 3, however, has the disadvantage that it needs to becontrolled at a numbe of different places.

The disadvantage is overcome by using the control system shown inFIGURES 12 to 14. This control system is mounted directly on a frame 52of the casting machine. The tundish assembly 13 is supported by acontrol frame 53 made of angle iron. The frame 53 is raised and loweredby means of four hydraulic cylinders 55 having pis tons 54. The liftingstroke in this example is mm. The pistons 54 are all liftedsimultaneously by means of a pump, such as for instance a manuallyoperated pump 56 that delivers through an equalizing valve 57. Thelowering movement is elfected by the weight of the assembly acting onthe pistons 54, and the return flow of the oil to the tank 58 iscontrolled by a control valve 59. With this arrangement, the controlframe 53 can be operated from a single operating station, and can beheld in place at any desired height.

FIGURES 15, 16 and 17 show a modification in which instead of thetundish assembly being movable upwards and downwards, the mold ismovable. In this modification there is a mold 60, a float 61 and atundish 62 with two feed nozzles 63. The mold 60 rests on two beams 64the ends of which are connected to a frame 65 which is itself connectedby brackets 66 to hydraulic lifting devices 67 in such a way thatactuation of the lifting devices 67 raises and lowers the frame 65 asrequired. The tundish 62 is supported by bars 68 that are supported, inturn, by fixed beams 69.

The hydraulic lifting devices 67 and the beams 69 are supported by aframe 70 which rests on the upper part of a housing 71 of the continuouscasting machine. The pouring spout has been omitted from the drawing forthe sake of greater clarity. The lifting devices 67 have in this examplea lifting stroke of 100 mm. Pistons of the lifting devices 67 aresimultaneously lifted by a pump such as a manual pump 72 which deliversthrough a pressure equalizing valve 73, so that the mold 60 is raised orlowered to bring it to the required height relative to the feed nozzles63 and thus relative to the tundish, The lowering of the mold iseffected by the weight of the mold assembly on the pistons of thelifting devices 67, and the return flow of oil into an oil tank 74 iscontrolled by a control valve 75.

The strand is usually lowered into water, the surface of which can bebrought to within about 10 cm. of the bottom edge of the mold. Coolantsother than water can of course be used if desired and further jets ofwater can be used for directly cooling the strand.

I wish it to be understood that I do not desire to be limited to theexact details of construction shown and described, for obviousmodifications will occur to a person skilled in the art.

Having thus described the invention, what I claim as new and desire tobe secured by Letters Patent is as follows:

1. In a process for continuously casting non-ferrous metal strand,particularly aluminum and aluminum alloys, with the aid of a tundishhaving at least one nozzle pouring the molten metal into a verticalopen-ended mold in which the flow of metal through the nozzle andthereby the height above the mold bottom of the meniscus level in themold is controlled by a float in the liquid metal in the mold, whereinthe casting operation is begun with the lowering of a dummy barinitially closing the bottom of the mold, the steps comprising, locatingduring the beginning of the casting operation the nozzle and the floatso far above the bottom of the mold as to ensure that the molten metalrises in the mold to a level sufiiciently high so that the float remainsfree from freezing into the solidifying metal and subsequently, shortlyafter the dummy bar together with the forming metal strand began thecasting operation by moving downwards, reducing the distance between thenozzle and the bottom of the mold for more than 10 mm., to a reducedheight desired for the remainder of the casting operation.

2. A process according to claim 1 in which the height of the meniscuslevel above the mold bottom is adjusted by vertically moving the mold.

3. A process according to claim 1, in which the height of the meniscuslevel above the mold bottom is adjusted by vertically moving thetundish.

4. A process according to claim 1, in which the distance between thelevel of the meniscus relative to the mold bottom is adjusted byvertically moving both the mold and the tundish.

5. A process according to claim 1 for the casting of aluminum slabs oflarge cross-section in which the height of the meniscus level at thebeginning is from 60 to 80 mm. above the bottom of the mold, and issubsequently reduced to from 25 to 40 mm.

6. A process according to claim 1, for the casting of slabs forsubsequent rolling or round bar in which the height of the meniscuslevel above the bottom at the mold is reduced after the strand hasemerged from the mold for a distance of about 5 cm.

7. A process according to claim 1, for the casting of aluminum slabshaving a cross-section of at least 800 x 150 mm., the steps of coolingthe mold and the strand in such a way that the sump of molten metal inthe mold is substantially rectangular as seen from above and thethickness of the solidified skin within the mold is substantially thesame along both the long and short sides of the strand.

References Cited UNITED STATES PATENTS 15 J. SPENCER OVERHOLSER, PrimaryExaminer.

R. SPENCER ANNEAR, Assistant Examiner.

US. Cl. X.R.

